This is weird. Marbled crayfish.

[Michigan Swamp Buck]

They're a problem in a cemetery?  Don't these things live in water?

Sounds like the cemetery has bigger problems than crayfish.  

When I lived in the suburbs of Detroit, I grew up in a neighborhood that had been a swamp at one time. There was a small field near the house that had some low areas and pits that kids dug for underground forts that filled with water.

These low spots flooded in the spring long enough to allow the crayfish to reproduce. Then by summer when the pools evaporated, the crayfish dug tunnels and capped them off with mud and lived below the waterline. The field was covered with those crayfish holes in early summer. Interestingly enough, the field was just big enough to support a large population of garter snakes that relied on the pits and crayfish holes to hibernate in during winter.

When I was really young that field had breeding toads, crayfish, garter snakes and these huge horse leeches in the wet areas. It was about a 1/4 mile long and about three or four city lots wide. There were other larger lots near there as well, it was like it in those lots too. This was in the 70's, it's totally built up now except for some larger private lots that are still there.

So I can see how crayfish could live on a large city lot, in a low spot on a lawn that floods in the spring long enough to reproduce before they burrow under for the rest of the year. They don't need a constantly flowing year round water source if the water table is high enough.